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Ronald L. Crawford - One of the best experts on this subject based on the ideXlab platform.
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Transformations of Toxic Metals and Metalloids by Pseudomonas stutzeri Strain KC and its Siderophore Pyridine-2,6-bis(Thiocarboxylic Acid)
Soil Biology, 2009Co-Authors: Anna M. Zawadzka, Andrzej Paszczynski, Ronald L. CrawfordAbstract:Pyridine-2,6-bis(Thiocarboxylic Acid)Pyridine-2,6-bis(Thiocarboxylic Acid) (pdtc)(pdtc) is a siderophore produced by Pseudomonas stutzeri KCPseudomonas stutzeri KC that plays a role in conditioning the bacterial environment. It serves as a siderophore in solubilizing ferric iron and other micronutrient metals, and as a thiol-containing compound, it reacts with toxic heavy metals and metalloids, reducing metals like Cr(VI), Se(IV), and Te(IV) and precipitating metals as sulfides (e.g., Hg(II), Cd(II), Pb(II), and As(III)), rendering them insoluble and less toxic. Understanding the mechanism by which bacteria use pdtc to interact with metals may contribute to our understanding of metal cycling in the biosphere, and may have potential for use in bioremediationbioremediation of heavy metals.
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Pyridine-2,6-bis(Thiocarboxylic Acid) Produced by Pseudomonas stutzeri KC Reduces Chromium(VI) and Precipitates Mercury, Cadmium, Lead and Arsenic
BioMetals, 2007Co-Authors: Anna M. Zawadzka, Ronald L. Crawford, Andrzej J. PaszczynskiAbstract:Interactions of the Pseudomonas stutzeri KC siderophore pyridine-2,6-bis(Thiocarboxylic Acid) (pdtc) with chromium(VI), mercury(II), cadmium(II), lead(II), and arsenic(III) are described. Pdtc was found to reduce Cr(VI) to Cr(III) in both bacterial cultures and in abiotic reactions with chemically synthesized pdtc. Cr(III) subsequently formed complexes with pdtc and pdtc hydrolysis products, and their presence was confirmed using electrospray ionization-mass spectrometry (ESI-MS). Cr(III):pdtc complexes were found to slowly release Cr(III) as chromium sulfide and possibly Cr(III) oxides. Pdtc also formed poorly soluble complexes with Hg, Cd, Pb, and As(III). Hydrolysis of those complexes led to the formation of their respective metal sulfides as confirmed by energy dispersive X-ray spectroscopy (EDS) elemental analysis. The pdtc-producing strain P. stutzeri KC showed higher tolerance to most of these metals as compared to a pdtc-negative mutant. A novel role of pdtc is postulated as its involvement in providing an extracellular pool of thiols that are used for redox processes in detoxification of the bacterial extracellular environment. These redox processes can be mediated by transition metal:pdtc complexes.
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Pyridine-2,6-Bis(Thiocarboxylic Acid) Produced by Pseudomonas stutzeri KC Reduces and Precipitates Selenium and Tellurium Oxyanions
Applied and environmental microbiology, 2006Co-Authors: Anna M. Zawadzka, Ronald L. Crawford, Andrzej PaszczynskiAbstract:Siderophores are iron-specific chelators that are produced and excreted by microorganisms under iron-limiting conditions as a part of an iron acquisition system. Some siderophores chelate metals other than iron, forming soluble or insoluble metal compounds and affecting the mobility and toxicity of those metals (8, 17, 47). Pyridine-2,6-bis(Thiocarboxylic Acid) (pdtc) is a siderophore produced by Pseudomonas stutzeri KC and P. putida DSM 3601 and DSM 3602 that has fortuitous carbon tetrachloride degradation activity (21, 30). Recent research has shown that pdtc promotes iron transport into the cell (25). P. stutzeri KC, its spontaneous pdtc-negative mutant CTN1, and other P. stutzeri strains also produce proferrioxamines (pFOs), which are probably their primary siderophores (A. Zawadzka et al., unpublished data). pdtc is a broad-range metal chelator; it chelates many transition metals, some heavy metals, lanthanides, and actinides. In general, micronutrient metals chelated by pdtc are soluble, while toxic metals form insoluble precipitates with pdtc (8, 39). Selenium and tellurium oxyanions are among the toxic metalloids precipitated by pdtc and pdtc-producing Pseudomonas stutzeri KC cultures. In nature selenium is present in igneous rocks and fossil fuels (19). The element is a metalloid that can exist in four oxidation states. Under aerobic conditions, selenium is present as toxic and soluble selenate (SeO42−) or selenite (SeO32−) or as insoluble and nontoxic elemental selenium (Se0). It is an essential micronutrient at low concentrations but is toxic at higher concentrations. Selenium is incorporated by organisms as selenide, and in high concentrations it substitutes for sulfur in cysteine and methionine, adversely affecting the integrity of proteins such as α-keratin and inhibiting the activity of enzymes such as glutathione peroxidase. Many bacteria have been shown to reduce selenite to Se0, thereby eliminating its toxicity (27, 34, 31); however, the mechanism of detoxification is unclear. Elemental selenium deposits were found in the cytoplasm (18, 19), in the periplasmic space (14), and outside the cells (48) of various organisms, suggesting that different mechanisms might be involved. Selenium can be reduced enzymatically by broad substrate-specific nitrate reductases (35), molybdenum-containing enzymes (4), or specific selenate reductases in an energy-conserving process (36). It has been suggested that the cellular pool of thiols, including glutathione (GSH), is involved in the reduction and resulting detoxification of both selenite and tellurite (18, 43). When all reduced GSH in a cell is converted to GS-Se-SG, the cell loses its principal reducing buffer and thus its nonspecific defense against selenium toxicity. Finally, sulfate-reducing bacterial (SRB) biofilms were found to precipitate elemental selenium and sulfur during sulfate-reducing growth as a nonspecific means of selenium removal (16). Tellurium is another highly toxic metalloid from group 16 of the periodic table. Tellurium is a relatively rare element found in nature in the form of metal tellurides (e.g., Pb, Cu, Ag, Au, and Sb). Industrial waste discharge sites can contain elevated concentrations of Te (2). Te(IV) as tellurite (TeO32−) is more toxic to most gram-negative bacteria than Se(IV) in the form of selenite. The MIC for bacteria lacking resistance determinants is in the order of 1 to 2 μg ml−1 for TeO32− (41) and 1 mg ml−1 for SeO32− (44). This is the reason tellurite was used as an antibacterial agent for the treatment of bacterial infections in the preantibiotic era and is still a component of some selective growth media (41). Bacterial resistance to tellurite is poorly understood but is thought to be associated with tellurite reduction and precipitation of metallic tellurium (27, 34, 38). It has been suggested that tellurite entering cells can be reduced by membrane-associated nitrate reductases (1, 35). Once inside the cell, glutathione and other thiol-carrying molecules are the main mediators of tellurite reduction (43, 45). Also, terminal oxidases of the respiratory chain in gram-negative bacteria are involved in the reduction of tellurite (42). Other mechanisms, including cysteine-metabolizing enzymes and methyl transferases, may be important resistance mechanisms against tellurite toxicity (3, 41). Finally, similarly to what occurs with selenite, tellurite reduction and precipitation by sulfate-reducing bacteria has been reported (27). Our current research investigated the nature of selenium and tellurium precipitates formed upon interaction with pdtc and the role of pdtc in detoxification of the bacterial environment. Here we propose a chemical mechanism for interactions of pdtc with selenite and tellurite. We identified the initial precipitates of Se and Te as insoluble selenides and tellurides of pdtc and the hydrolysis products of pdtc. Our data suggest that hydrolysis and oxidation of those initial precipitates leads to the formation of elemental Se and Te. We compared the reduction and precipitation products of selenite and tellurite mediated by synthetic, high-purity pdtc to the reaction products formed by pdtc-producing P. stutzeri KC and the pdtc-negative mutant strain CTN1. The nature of the precipitates formed in bacterial cultures of P. stutzeri KC was similar to the in vitro reaction products formed by synthetic pdtc. Electron microscopy analyses showed that in strain KC, elemental selenium and tellurium accumulated mainly extracellularly; however, pdtc did not completely prevent the accumulation of intracellular Se0 and Te0 under our experimental conditions. The use of pdtc by P. stutzeri KC to reduce selenite and tellurite is to our knowledge a unique system utilizing a siderophore to carry thiols to the extracellular environment that we describe here for the first time in bacteria. Our results add a novel function to the known activities of pdtc that is linked to detoxification of the bacterial habitat (5).
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Metal chelating properties of pyridine-2,6-bis(Thiocarboxylic Acid) produced by Pseudomonas spp. and the biological activities of the formed complexes
Biometals, 2002Co-Authors: Marc S. Cortese, Andrzej Paszczynski, Thomas A. Lewis, Jonathan L. Sebat, Vladimir Borek, Ronald L. CrawfordAbstract:We evaluated the ability of pyridine-2,6-bis(Thiocarboxylic Acid) (pdtc) to form complexes with 19 metals and 3 metalloids. Pdtc formed complexes with 14 of the metals. Two of these metal:pdtc complexes, Co:(pdtc)_2 and Cu:pdtc, showed the ability to cycle between redox states, bringing to 4 the number of known redox-active pdtc complexes. A precipitant formed when pdtc was added to solutions of As, Cd, Hg, Mn, Pb, and Se. Additionally, 14 of 16 microbial strains tested were protected from Hg toxicity when pdtc was present. Pdtc also mediated protection from the toxic effects of Cd and Te, but for fewer strains. Pdtc by itself does not facilitate iron uptake, but increases the overall level of iron uptake of Pseudomonas stutzeri strain KC and P. putida DSM301. Both these pseudomonads could reduce amorphous Fe(III) oxyhydroxide in culture. In vitro reactions showed that copper and pdtc were required for this activity. This reaction may derive its reducing power from the hydrolysis of the thiocarboxyl groups of pdtc.
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Structural, functional, and evolutionary analysis of moeZ, a gene encoding an enzyme required for the synthesis of the Pseudomonas metabolite, pyridine-2,6-bis(Thiocarboxylic Acid)
BMC evolutionary biology, 2002Co-Authors: Marc S. Cortese, Allan Caplan, Ronald L. CrawfordAbstract:Background Pyridine-2,6-bis(Thiocarboxylic Acid) (pdtc) is a small secreted metabolite that has a high affinity for transition metals, increases iron uptake efficiency by 20% in Pseudomonas stutzeri, has the ability to reduce both soluble and mineral forms of iron, and has antimicrobial activity towards several species of bacteria. Six GenBank sequences code for proteins similar in structure to MoeZ, a P. stutzeri protein necessary for the synthesis of pdtc.
Tom Lewis - One of the best experts on this subject based on the ideXlab platform.
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transcriptional regulation of the pdt gene cluster of pseudomonas stutzeri kc involves an arac xyls family transcriptional activator pdtc and the cognate siderophore pyridine 2 6 bis Thiocarboxylic Acid
Applied and Environmental Microbiology, 2006Co-Authors: Sergio E Morales, Tom LewisAbstract:In order to gain an understanding of the molecular mechanisms dictating production of the siderophore and dechlorination agent pyridine-2,6-bis(Thiocarboxylic Acid) (PDTC), we have begun characterization of a gene found in the pdt gene cluster of Pseudomonas stutzeri KC predicted to have a regulatory role. That gene product is an AraC family transcriptional activator, PdtC. Quantitative reverse transcription-PCR and expression of transcriptional reporter fusions were used to assess a role for pdtC in the transcription of pdt genes. PdtC and an upstream, promoter-proximal DNA segment were required for wild-type levels of expression from the promoter of a predicted biosynthesis operon (PpdtF). At least two other transcriptional units within the pdt cluster were also dependent upon pdtC for expression at wild-type levels. The use of a heterologous, Pseudomonas putida host demonstrated that pdtC and an exogenously added siderophore were necessary and sufficient for expression from the pdtF promoter, i.e., none of the PDTC utilization genes within the pdt cluster were required for transcriptional signaling. Tests using the promoter of the pdtC gene in transcriptional reporter fusions indicated siderophore-dependent negative autoregulation similar to that seen with other AraC-type regulators of siderophore biosynthesis and utilization genes. The data increase the repertoire of siderophore systems known to be regulated by this type of transcriptional activator and have implications for PDTC signaling.
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Identification and characterization of Pseudomonas membrane transporters necessary for utilization of the siderophore pyridine-2,6-bis(Thiocarboxylic Acid) (PDTC).
Microbiology, 2006Co-Authors: Lynne H. Leach, Tom LewisAbstract:The compound pyridine-2,6-bis(Thiocarboxylic Acid) (PDTC) is known to be produced and excreted by three strains of Pseudomonas. Its reactivity includes the complete dechlorination of the environmental contaminant carbon tetrachloride. PDTC functions as a siderophore; however, roles as a ferric reductant and antimicrobial agent have also been proposed. PDTC function and regulation were further explored by characterizing the phenotypes of mutants in predicted membrane transporter genes. The functions of a predicted outer-membrane transporter (PdtK) and a predicted inner-membrane permease (PdtE) were examined in Pseudomonas putida DSM 3601. Uptake of iron from 55Fe(III):PDTC, and bioutilization of PDTC in a chelated medium, were dependent upon PdtK and PdtE. Another strain of P. putida (KT2440), which lacks pdt orthologues, showed growth inhibition by PDTC that could be relieved by introducing a plasmid containing pdtKCPE. Transcriptional activation in response to exogenously added PDTC (25 μM) was unaltered by the pdtK or pdtE mutations; each mutant showed activation of a pdt transcriptional reporter, indistinguishable from an isogenic PDTC utilization-proficient strain. The data demonstrate that PdtK and PdtE constitute a bipartite outer-membrane/inner-membrane transport system for iron acquisition from Fe(III):PDTC. Disruptions in this portion of the P. putida DSM 3601 pdt gene cluster do not abolish PDTC-dependent transcriptional signalling.
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Transcriptional Regulation of the pdt Gene Cluster of Pseudomonas stutzeri KC Involves an AraC/XylS Family Transcriptional Activator (PdtC) and the Cognate Siderophore Pyridine-2,6-Bis(Thiocarboxylic Acid)
Applied and environmental microbiology, 2006Co-Authors: Sergio E Morales, Tom LewisAbstract:In order to gain an understanding of the molecular mechanisms dictating production of the siderophore and dechlorination agent pyridine-2,6-bis(Thiocarboxylic Acid) (PDTC), we have begun characterization of a gene found in the pdt gene cluster of Pseudomonas stutzeri KC predicted to have a regulatory role. That gene product is an AraC family transcriptional activator, PdtC. Quantitative reverse transcription-PCR and expression of transcriptional reporter fusions were used to assess a role for pdtC in the transcription of pdt genes. PdtC and an upstream, promoter-proximal DNA segment were required for wild-type levels of expression from the promoter of a predicted biosynthesis operon (PpdtF). At least two other transcriptional units within the pdt cluster were also dependent upon pdtC for expression at wild-type levels. The use of a heterologous, Pseudomonas putida host demonstrated that pdtC and an exogenously added siderophore were necessary and sufficient for expression from the pdtF promoter, i.e., none of the PDTC utilization genes within the pdt cluster were required for transcriptional signaling. Tests using the promoter of the pdtC gene in transcriptional reporter fusions indicated siderophore-dependent negative autoregulation similar to that seen with other AraC-type regulators of siderophore biosynthesis and utilization genes. The data increase the repertoire of siderophore systems known to be regulated by this type of transcriptional activator and have implications for PDTC signaling. The bacterial strain Pseudomonas stutzeri KC excretes the secondary metabolite and transition metal chelator pyridine 2,6-bis(thiocarboxylate) (PDTC) under iron-limited growth conditions. PDTC is also the active agent of the cometabolic dechlorination of carbon tetrachloride (CCl4) displayed by that organism (21). In order to reliably exploit this activity for remediation of CCl4 contamination, an understanding of factors affecting PDTC production is necessary. PDTC is a siderophore, a class of compounds whose production has evolved among bacteria and other organisms for the acquisition of iron (14). The regulation of siderophore production is a component of iron homeostasis, which involves balancing avid uptake capabilities with the avoidance of iron-catalyzed oxidative damage (3).
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Carbon tetrachloride dechlorination by the bacterial transition metal chelator pyridine-2,6-bis(Thiocarboxylic Acid).
Environmental science & technology, 2001Co-Authors: Tom Lewis, Andrzej Paszczynski, Scott W. Gordon-wylie, Shanti Jeedigunta, Chang-ho Lee, Ronald L. CrawfordAbstract:A reaction pathway is proposed to explain the formation of end products during defined chemical reactions between carbon tetrachloride (CCl4) and either metal complexes of pyridine-2,6-bis(Thiocarboxylic Acid) (PDTC) or pure cultures of Pseudomonas stutzeri KC. The pathway includes one-electron reduction of CCl4 by the Cu(II):PDTC complex, condensation of trichloromethyl and thiyl radicals, and hydrolysis of a labile thioester intermediate. Products detected were carbon dioxide, chloride, carbonyl sulfide, carbon disulfide, and dipicolinic Acid. Spin-trapping and electrospray MS/MS experiments gave evidence of trichloromethyl and thiyl radicals generated by reaction of CCl4 with PDTC and copper. Experiments testing the effects of transition metals showed that dechlorination by PDTC requires copper and is inhibited by cobalt but not by iron or nickel. PDTC was shown to react stoichiometrically rather than catalytically without added reducing equivalents. With added reductants, an increased turnover was seen along with increased chloroform production.
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A Pseudomonas stutzeri gene cluster encoding the biosynthesis of the CCl4-dechlorination agent pyridine-2,6-bis(Thiocarboxylic Acid).
Environmental microbiology, 2000Co-Authors: Tom Lewis, Chang-ho Lee, Marc S. Cortese, Jonathan Sebat, Tonia L. Green, Ronald L. CrawfordAbstract:A spontaneous mutant of Pseudomonas stutzeri strain KC lacked the carbon tetrachloride (CCl4) transformation ability of wild-type KC. Analysis of restriction digests separated by pulsed-field gel electrophoresis (PFGE) indicated that the mutant strain CTN1 differed from strain KC by deletion of approximately 170 kb of chromosomal DNA. CTN1 did not produce pyridine-2,6-bis(Thiocarboxylic Acid) (PDTC), the agent determined to be responsible for CCl4 dechlorination in cultures of strain KC. Cosmids from a genomic library of strain KC containing DNA from within the deleted region were identified by hybridization with a 148 kb genomic SpeI fragment absent in strain CTN1. Several cosmids identified in this manner were further screened for complementation of the PDTC biosynthesis-negative (Pdt−) phenotype. One cosmid (pT31) complemented the Pdt− phenotype of CTN1 and conferred CCl4 transformation activity and PDTC production upon other pseudomonads. Southern analysis showed that none of three other P. stutzeri strains representing three genomovars contained DNA that would hybridize with the 25 746 bp insert of pT31. Transposon mutagenesis of pT31 identified open reading frames (ORFs) whose disruption affected the ability to make PDTC in the strain CTN1 background. These data describe the pdt locus of strain KC as residing in a non-essential region of the chromosome subject to spontaneous deletion. The pdt locus is necessary for PDTC biosynthesis in strain KC and is sufficient for PDTC biosynthesis by other pseudomonads but is not a common feature of P. stutzeri strains.
Eoin M. Scanlan - One of the best experts on this subject based on the ideXlab platform.
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Rapid Access to Thiolactone Derivatives through Radical-Mediated Acyl Thiol-Ene and Acyl Thiol-Yne Cyclization.
Organic letters, 2018Co-Authors: Ruairí O. Mccourt, Fabrice Dénès, Goar Sánchez-sanz, Eoin M. ScanlanAbstract:A new synthetic approach to thiolactones that employs an efficient acyl thiol–ene (ATE) or acyl thiol–yne (ATY) cyclization to convert unsaturated Thiocarboxylic Acid derivatives into thiolactones under very mild conditions is described. The high overall yields, fast kinetics, high diastereoselectivity, excellent regiocontrol, and broad substrate scope of these reaction processes render this a very useful approach for diversity-oriented synthesis and drug discovery efforts. A detailed computational rationale is provided for the observed regiocontrol.
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Rapid Access to Thiolactone Derivatives through Radical-Mediated Acyl Thiol–Ene and Acyl Thiol–Yne Cyclization
2018Co-Authors: Ruairi O. Mccourt, Goar Sánchez-sanz, Fabrice Dénès, Eoin M. ScanlanAbstract:A new synthetic approach to thiolactones that employs an efficient acyl thiol–ene (ATE) or acyl thiol–yne (ATY) cyclization to convert unsaturated Thiocarboxylic Acid derivatives into thiolactones under very mild conditions is described. The high overall yields, fast kinetics, high diastereoselectivity, excellent regiocontrol, and broad substrate scope of these reaction processes render this a very useful approach for diversity-oriented synthesis and drug discovery efforts. A detailed computational rationale is provided for the observed regiocontrol
James P. Tam - One of the best experts on this subject based on the ideXlab platform.
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Acyl disulfide-mediated intramolecular acylation for orthogonal coupling between unprotected peptide segments. Mechanism and application
Tetrahedron Letters, 1996Co-Authors: Chuan-fa Liu, Chang Rao, James P. TamAbstract:A highly efficient orthogonal coupling approach for peptide bond formation using unprotected peptide segments was described. The key element of this approach consisted of capturing an Npys modified N-Cys side-chain thiol of the amino segment with a Cα-Thiocarboxylic Acid of the acyl segment to form an acyl disulfide which undergoes rapid intramolecular acylation to generate an amide bond. A final product with a native Cys residue at the ligation site was obtained after a thiolytic reduction step.
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Peptide synthesis using unprotected peptides through orthogonal coupling methods.
Proceedings of the National Academy of Sciences of the United States of America, 1995Co-Authors: James P. Tam, Chuan-fa Liu, Jun ShaoAbstract:Abstract We describe an approach to the synthesis of peptides from segments bearing no protecting groups through an orthogonal coupling method to capture the acyl segment as a thioester that then undergoes an intramolecular acyl transfer to the amine component with formation of a peptide bond. Two orthogonal coupling methods to give the covalent ester intermediate were achieved by either a thiol-thioester exchange mediated by a trialkylphosphine and an alkylthiol or a thioesterification by C alpha-Thiocarboxylic Acid reacting with a beta-bromo amino Acid. With this approach, unprotected segments ranging from 4 to 37 residues were coupled to aqueous solution to give free peptides up to 54 residues long with high efficiency.
Thomas A. Lewis - One of the best experts on this subject based on the ideXlab platform.
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The role of the siderophore pyridine-2,6-bis (Thiocarboxylic Acid) (PDTC) in zinc utilization by Pseudomonas putida DSM 3601
BioMetals, 2007Co-Authors: Lynne H. Leach, James C. Morris, Thomas A. LewisAbstract:Previous work had suggested that in addition to serving the function of a siderophore, pyridine-2,6-bis(Thiocarboxylic Acid) (PDTC) may also provide producing organisms with the ability to assimilate other divalent transition metals. This was tested further by examining regulation of siderophore production, expression of pdt genes, and growth in response to added zinc. In media containing 10–50 μM ZnCl_2, the production of PDTC was found to be differentially repressed, as compared with the production of pyoverdine. The expression of PdtK, the outer membrane receptor involved in PDTC transport, was also reduced in response to added zinc whereas other iron-regulated outer membrane proteins were not. Expression of a chromosomal pdt I:: xyl E fusion was repressed to a similar extent in response to zinc or iron. Mutants that cannot produce PDTC did not show a growth enhancement with micromolar concentrations of zinc as seen in the wild type strain. The phenotype of the mutant strains was suppressed by the addition of PDTC. The outer membrane receptor and inner membrane permease components of PDTC utilization were necessary for relief of chelator (1,10-phenanthroline)-induced growth inhibition by Zn:PDTC. Iron uptake from ^55Fe:PDTC was not affected by a 32-fold molar excess of Zn:PDTC. The data indicate that zinc present as Zn:PDTC can be utilized by strains possessing PDTC utilization functions but that transport is much less efficient than for Fe:PDTC.
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personal correspondence
2003Co-Authors: Lynne H. Leach, Thomas A. LewisAbstract:Identification and characterization of Pseudomonas membrane transporters necessary for utilization of the siderophore pyridine-2,6-bis(Thiocarboxylic Acid) (PDTC
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Metal chelating properties of pyridine-2,6-bis(Thiocarboxylic Acid) produced by Pseudomonas spp. and the biological activities of the formed complexes
Biometals, 2002Co-Authors: Marc S. Cortese, Andrzej Paszczynski, Thomas A. Lewis, Jonathan L. Sebat, Vladimir Borek, Ronald L. CrawfordAbstract:We evaluated the ability of pyridine-2,6-bis(Thiocarboxylic Acid) (pdtc) to form complexes with 19 metals and 3 metalloids. Pdtc formed complexes with 14 of the metals. Two of these metal:pdtc complexes, Co:(pdtc)_2 and Cu:pdtc, showed the ability to cycle between redox states, bringing to 4 the number of known redox-active pdtc complexes. A precipitant formed when pdtc was added to solutions of As, Cd, Hg, Mn, Pb, and Se. Additionally, 14 of 16 microbial strains tested were protected from Hg toxicity when pdtc was present. Pdtc also mediated protection from the toxic effects of Cd and Te, but for fewer strains. Pdtc by itself does not facilitate iron uptake, but increases the overall level of iron uptake of Pseudomonas stutzeri strain KC and P. putida DSM301. Both these pseudomonads could reduce amorphous Fe(III) oxyhydroxide in culture. In vitro reactions showed that copper and pdtc were required for this activity. This reaction may derive its reducing power from the hydrolysis of the thiocarboxyl groups of pdtc.
